The ultrafast all-optical solid-state framing camera(UASFC) technique is a new diagnostic method based on the semiconductor photorefractive effect. The ultra-fast response characteristics of this method are mainly determined by the response time of the semiconductor material's photorefractive index change. How to quickly and accurately measure the photorefractive index response time of semiconductor materials is an important step in the development of all-optical solid ultra-fast diagnostic chip. In this paper, the 100fs pulsed laser is divided into two beams. One of which is used as excitation light to generate pulsed X-ray source; the other beam is measured as a spectral probe light. Through the test of GaAs material, the response time of the refractive index change of GaAs material was less than 5ps, which laid a foundation for further optimization experiment and accurate measurement.
The ultrafast all-optical solid-state framing camera(UASFC) based on semiconductor photorefractive effect is a new type of X-ray ultrafast imaging system. The temporal resolution of UASFC is determined by the response time of the semiconductor. We improve the pump-probe experiment to measure the time response of GaAs/AlGaAs. In our recent experiments, the full width of half maximum (FWHM) is about 2ps, and the dynamic test result of the UASFC system, which use these AlGaAs samples, is 2.5ps. The results verify feasibility of the measurement and provide necessary methods for the further construction of high performance UASFC system.
Highly photo-excited layer thickness in GaAs is measured using a pump probe arrangement. A normally incident pump illumination spatially modulated by a mask will induce a corresponding refractive index change distribution in the depth direction due to edge scattering and attenuation absorption effect, which can deflect the probe beam passing through this excited region. Maximum deflection of the probe beam will be limited by the thickness of excited layer, and thus can also be employed to measure the thickness of the photo-excited layer of the material. Theoretical calculation confirms the experimental results. This method can find its application in measurements of photo-excited layer thickness of many kinds of materials and be significant to study the characteristics of materials in laser machining, grating and waveguide fabricating.
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